This invention relates to insulated electrical terminal assemblies and more particularly relates to such assemblies suitable for use in making electric connections on a battery-powered truck or similar apparatus that subjects the electric terminals thereon to extensive vibration, thermal cycling, and exposure to contaminants.
It is generally well known to provide various types of electrical terminal assemblies for connecting internal circuit components to other electrical devices located externally of an apparatus. For example, in the manufacture of battery-powered vehicles of the kind for which the present invention is particularly well suited, it is known to mount electric motor connection terminal assemblies on an appropriate part of a motor housing or other suitable support structure in order to provide convenient means for making electrical connections between the drive motor windings and a plurality of interconnected batteries or other power source for the motor. Typically, such a terminal includes a knurled brass stud that is within a dielectric sleeve to insulate the stud from the motor housing. The stud and sleeve assembly is then characteristically glued into an aperture in the motor frame so that the motor windings can be connected to one end of the stud, while a battery terminal lead is connected to the other end of the stud, which extends beyond the outer surface of the frame or housing.
Although such conventional electric terminal assemblies have provided satisfactory service for years, it has been found that they also present a number of disadvantages. Such disadvantages can be manifested during both the initial manufacture and installation of such terminal assemblies, and in the use and operation of the terminals in the field. Perhaps the most common disadvantage of such prior art terminal assemblies is that the glued connections in them can be broken in manufacturing operations when assembly connections are made by tightening bolts into the inner end of the studs to fasten motor windings to the terminal. Because such assembly operations are usually done manually, the torque forces applied vary from installer to installer and even the same installer will often apply different torque forces on separate assemblies. Even if such breakage does not occur in the manufacture of the previously known, glue-fastened type of terminal assemblies, their use is undesirably expensive due to the relatively long cure cycles needed to properly set the adhesive bonds on the inner and outer surfaces of the dielectric sleeves. In addition to such manfacturing problems with those earlier terminal assemblies, the glued components can be relatively easily broken apart in the field responsive to a bolt or nut being tightened down on a terminal to connect a battery lead or other power source to the outer end of the terminal. Again, such connections are manually made, so torque forces may vary in a wide, and uncontrolled, range from one installer to another.
Because of the normal need to mount such terminals through apertures in a curved motor housing or similar curved supporting surface, it has often been difficult to make a suitably strong mechanical connection between the dielectric sleeve of the terminal assembly and the housing, except by use of the glued-type of connnections mentioned above. Moreover, the search for a satisfactory solution to such known disadvantages was complicated by the need to employ dielectric materials for the sleeves that have coefficients of expansion close to those of the stud portion of the terminal assembly, while at the same time affording adequate resistance to thermal and electrical shock and to deterioration from contaminants, in order to make such terminals adaptable for operation on battery trucks and similar rugged-duty apparatus.
Another problem often encountered in the application of prior art plastic terminal assemblies is that when devices, such as motor housings, on which the terminals are mounted, happen to be dropped, jolted or otherwise mishandled, the terminal assembly is frequently cracked or otherwise damaged. The present invention affords a terminal assembly structure that is much more resistant to damage as a consequence of mishandling. Specifically, in one form of the invention a reinforcing ring is molded into the fastening nut of a terminal assembly to enable the nut to endure about fifty percent higher torquing forces than it could endure without such a ring. In addition, the molded-in ring prevents nuts from undesirably opening up when the plastic of the nuts becomes cracked.